Field of the Invention
The present invention relates to a consumable electrode type welding method for generating an arc between a welding wire serving as a consumable electrode and a welding base metal serving as a member to be welded to thereby control the welding output.
Description of Related Art including information disclosed under 37 C.F.R. 1.97 and 1.98.
Recently, the welding industry has always made effort to further enhance the productivity of the welding operation in order to secure an international competitive ability.
Especially, there have been increasing the need for a reduction in a so called “unexpected stop”, which is a slight trouble causing the production line to stop, and the need for a reduction in the tact time more than before.
As the reasons for the unexpected stop, there can be pointed out various reasons and the greatest reason is a trouble caused by fault in an arc start.
In view of this, in a conventional consumable electrode type welding method, as a method for enforcing its arc start, there is known the following method: that is, when a start signal is input from the outside, a robot manipulator is moved to thereby move a welding torch to a previously instructed welding start position and after then, while the feeding of the welding wire remains stopped, the welding torch is moved substantially in the welding wire feed direction by the robot manipulator to thereby allow the leading end of the welding wire to approach the member to be welded; if it is detected that the welding wire leading end has come into contact with the member to be welded, an initial current of a preset small current value is applied from a welding power supply device and, at the same time, the welding torch is moved in the opposite direction to the substantially welding wire feed direction to thereby carry out the retreating movement of the welding torch which moves the welding wire leading end away from the member to be welded; if the welding wire leading end and the member to be welded are moved away from each other due to the retreating movement of the welding torch, there is generated an arc to which the initial current is applied and, while the initial arc generating state remains held, the retreating movement of the welding torch is allowed to continue; if the welding torch returns back to the welding start position, the retreating movement is switched over to the movement in the previously instructed welding direction and, at the same time, the feed of the welding wire is started and a steady-state welding current is applied, whereby the initial arc generating state is switched over to the steady-state arc generating stage. (For example, see the patent literature 1).
Now, FIG. 5 is a schematic block diagram of the whole of a welding system for enforcing the above-mentioned consumable electrode type welding method using a robot.
In FIG. 5, reference character 101 designates a welding wire used as a consumable electrode; and, the welding wire 101 can be played out from a wire spool 102 in the direction of a welding torch 104 by a wire feed motor 103. Reference numeral 105 stands for a welding power supply device. The welding power supply device 105 applies a given welding current I and a given welding voltage V, through the welding torch 104 and welding tip 106, into between the welding wire 101 and a base metal 107 serving as a member to be welded to thereby generate an arc 108 and control the wire feed motor 103 for enforcing the welding operation.
Reference numeral 109 designates a robot manipulator. The robot manipulator 109 holds the welding torch 104, positions the torch 104 at a welding start position (not shown) and moves the welding torch 104 along a welding line (not shown).
Also, the robot manipulator 109 is controlled by a robot control unit 110. The robot control unit 110 executes a two-way communication S between the welding power supply device 105 and itself and thus the robot control unit 110 sends welding conditions such as the welding current I and welding voltage V as well as instruction signals such as a welding start signal and a welding end signal.
Now, description will be given below of a consumable electrode type welding method used in the above-structured system with reference to a timing chart shown in FIG. 6.
Referring to FIG. 6 specifically, in the vertical direction thereof, there are shown the respective states of the moving speed of the welding torch TV, the feeding speed of the welding wire WF, a short circuit detect signal A/S, a welding current I and a welding voltage V, whereas the horizontal axis thereof expresses time. In this illustration, as timings, TSO′ designates a timing when a welding start signal is transmitted from the robot control unit 110 to the welding power supply device 105, while TS1′-TS5 40 following TSO′ stand for timings in the course of time respectively.
Firstly, the robot control unit 110 not only transmits a welding start signal to the welding power supply device 105 but also actuates the robot manipulator 109 to accelerate the welding torch 104 toward the base metal 107. And, when the speed of the welding torch 104 reaches an initial torch speed TV0, the robot control unit 110 causes the acceleration of the robot manipulator 109 to stop and continues the lowering motion of the welding torch 104 at a constant speed.
Also, when receiving the welding start signal from the robot control unit 110, the welding power supply device 105 applies a no-load voltage VO′ into between the welding wire 101 and base metal 107.
Then, at the timing TS1′, if the welding wire 101 is contacted with the base metal 107, short circuit detect means (not shown) provided in the inside of the welding power supply device 105 outputs a short circuit signal A/S.
This short circuit detect signal A/S is transmitted through the two-way communication S to the robot control unit 110 and thus the robot control unit 110 reduces and stops the robot manipulator 109 immediately, so that, at the timing TS2′, the operation of the robot manipulator 109 is caused to stop, that is, the speed of the welding torch 104 becomes zero.
After then, the robot control unit 110 immediately reverses the operation of the robot manipulator 109 and starts the operation thereof in a direction where the welding torch 104 is pulled apart from the base metal 107, thereby lifting the welding torch 104.
The period extending from the timing TS1′ to TS3′ is a short circuit period and, in this period, during the time until the timing TS2′ where the robot manipulator 109 reduces down to zero, the welding wire 101 is pressed against the base metal 107; but, from the timing TS2′ on, since the operation of the robot manipulator 109 is reversed, the pressing amount of the welding wire 101 decreases and thus, at the timing TS3′, the short circuit is removed.
The timing, that is, the timing TS3′ occurs at the time when the area of a triangle cde, which is shown by the line of the speed TV of the welding torch and expresses the lifting amount of the welding wire 101, exceeds the area of a triangle abc which is shown by the line of the speed TV of the welding torch for expressing the pressing amount of the welding wire 101.
Here, when the initial short circuit occurs at the timing TS1′, the welding power supply device 105 controls the welding current I at I1′, and then increases the current up to I2′ after passage of a given time and waits for the opening of the short circuit.
As the first stage of the initial short circuit period, the welding current is controlled to I1′ which is set relatively low. The reason for this is to avoid a possibility that, owing to the initial short circuit, the leading end portion of the welding wire is heated due to Joule effect to melt the wire and thus, simultaneously with generation of the arc, the molten welding wire can spatter around to form spatters.
Also, to change the current from I1′ to I2′ is to be able to apply energy enough to generate the arc when the short circuit is opened at the timing TS3.
When an arc is generated at the timing TS3, the welding power supply device 105 actuates the wire feed motor 103 to accelerate the welding wire 101 toward the base metal 107, continues the acceleration until the speed of the welding wire 101 reaches a welding wire speed (not shown) for actual welding, and, after the welding wire speed reaches the welding wire speed for actual welding, continues the feeding of the welding wire at a constant speed.
Also, after controlling the arc current I to an arc initial current I3′ for a given time in linking with the actuation of the wire feed motor 103, the welding power supply device 105 controls the current to a second initial current I4 and, after then, controls the current to an output for actual welding (not shown).
Next, description will be given below of a welding end time in the above-mentioned consumable electrode type welding method in the welding system with reference to a timing chart shown in FIG. 7.
Referring to FIG. 6 specifically, in the vertical direction thereof, there are shown the respective states of the moving speed of the welding torch TV, the feeding speed of the welding wire WF and a welding output P, whereas the horizontal axis thereof expresses time. In this illustration, as timings, TEO′ designates a timing when a welding end signal is transmitted from the robot control unit 110 to the welding power supply device 105, while TE1′-TE4′following TEO′ stand for timings in the course of time respectively.
Firstly, when receiving a welding end signal from the robot control unit 110, the welding power supply device 105 controls the wire feed motor 103 to reduce the feed speed of the welding wire 101.
Simultaneously with this feed speed reduction of the welding wire, the welding power supply device 105 reduces the welding output and, at a timing TE2′ where a predetermined condition is satisfied, it controls the welding output to a constant welding output.
This constant output PI is referred to as a “burn-back”. Generally, the welding power supply device 105 continues the burn-back at and from a timing TE3′ where the welding wire 101 is caused to stop, that is, keeps the constant output to continue the ark 108 for a given period; and, after the welding wire 101 is burned up, the welding power supply device 105 stops the constant output at a timing TE4′.
This “burn-back” control method is a widely used control method for preventing occurrence of a so called wire stick phenomenon in which the welding wire 101 is contacted with a molten pool (not shown) and is thereby fixed when the welding is ended.
Patent literature: JP 2002-205169 publication
However, the conventional consumable electrode type welding method requires the reversing operation of the robot manipulator 109.
That is, when it is detected that the leading end of the welding wire 101 is contacted with the base metal 107, the reduction of the speed of the robot manipulator 109 moving forwardly is started, the forward movement of the robot manipulator 109 is the caused to stop once, and, after then, the operation of the robot manipulator 109 is reversed and accelerated in the backward direction, which requires not only the response time of the robot manipulator 109 but also the acceleration and reduction times thereof.
Also, since the wire feed motor 103 is actuated for the first time after generation of the initial arc, the feed of the welding wire 101 is not be able to catch up with the melting speed of the welding wire 101 to thereby extend the length of the arc 108, resulting in the unstable arc 108.
And, in the welding end time, to prevent the “wire stick” phenomenon, there is necessary the “burn-back” processing, which takes time for execution of this processing, so that the tact time is extended. Also, there is formed a ball-like fixed body in the leading end of the welding wire 101 due to the burnt-up of the welding wire 10, which obstructs the arc start in the next step.
Thus, it is an object of the invention to provide a consumable electrode type welding method which can reduce the waste time found in the conventional consumable electrode type welding method, can hold the proper length of an arc after generation of the arc to thereby stabilize the arc in the welding start part, and can positively prevent the occurrence of the wire stick phenomenon and can hold the wire leading end portion in a proper shape, thereby being able to carry out a proper arc start in the next step.